The invention relates to a method to verify the efficiency of anti-jamming by antenna processing in one or more space communications on board a geostationary satellite, as well as its implementation from the ground.
The invention can be applied in anti-jamming for space telecommunications and is a tool of assistance in optimizing the planning of connection bit rates in a theatre of operations depending on jamming conditions.
At present, anti-jamming by antenna processing is the most efficient way to protect one or more space or radio communications links against hostile jamming units. Anti-jamming by antenna processing consists in implementing what is called an adaptive antenna at reception. The chief property of this adaptive antenna is that it matches its radiation pattern in real time to the received signal, setting pattern holes toward the jamming units while at the same time maintaining sufficient gain in the direction of the link or links to be protected as can be seen in FIG. 1. This result can be obtained from a minimum amount of information on the links to be protected such as knowledge of the position of the transmitters, the theatre of operations or the learning sequences conveyed by the transmitters without a priori knowledge of the jamming units present. However, in certain cases, the a priori estimation of the positions of the jamming units may be advantageously used by the adaptive antenna so as to simplify the processing operations.
FIG. 2 shows an adaptive antenna with a purely spatial structure. It is formed by an network of sensors Ci or radiating elements, a set of digital or analog reception chains CRi, downstream from the sensors, a set of adaptive filters Fi with one complex coefficient per filter whose role is to carry out the phase and amplitude weighting of the signals coming from the difference sensors before summation, and an adaptive algorithm A whose role is to carry out the real-time matching of the coefficients of the adaptive filters so as to optimize a criterion as a function of the information available a priori on the signals of interest and therefore the application.
The adaptive antenna can be implemented in an analog, digital or hybrid way. In the first case, the weightings are computed and applied analogically while, in the second case, they are computed and applied digitally. In the third case, the set of complex weightings is computed digitally and copied analogically before summation.
For a digital implantation, the adaptive filters are formed by complex weighting operations whereas, for an analog implantation, these filters are formed by the cascade connection of a phase-shifter and a variable attenuator or a hybrid quadrature as can be shown in FIG. 3. In the context of space communications, when there are no jamming units, the set of weightings synthesizes a coverage (or a spot) on the earth, centered on a given point and having a certain surface area as can be seen in FIG. 4. In general, the coverage is characterized especially by the 3 dB width of the beam formed by the set of weightings. According to the size of this 3 dB lobe width or width of the illuminated surface area of the earth, we may speak of theatre, regional or global coverage, the latter corresponding to coverage of the entire earth. The working stations are deployed inside a coverage considered for a given mission and communicate together and/or with the mainland by satellite.
A jamming operation from one or more terrestrial regions jams the useful uplinks (from the earth to a satellite) and it is the role of the adaptive antenna precisely to carry out anti-jamming on the links by creating antenna pattern holes toward the jamming units, located outside or within the coverage and picked up respectively by the minor or major lobes of the antenna.